Room air conditioning units are employed to provide temperature control of a room. When transferring heat from outdoors into the room, the efficiency of a heat pump can be measured by the coefficient of performance (COP), which is found by dividing the outdoor heat supplied by the heat pump to the room by the amount of energy used to supply that heat. Both the heating capacity and the COP of a heat pump are reduced as the outdoor temperature drops. The outdoor temperature at which the heat capacity of the heat pump is equal to the heat loss of the room is called the “balance point.” When the outdoor temperature is less than balance point, supplemental heaters are needed to generate the heat required to reach the desired room temperature.
Some supplemental heating approaches burn natural gas or petroleum-based fuels to generate supplemental heat, but some areas do not have easy access to natural gas or petroleum-based fuels, or it is dangerous to store the highly combustible natural gas or fuels. Another supplemental heating approach uses an electric wire with a predetermined resistance to generate heat, but this approach results in units that require costly heat shields and safety concerns. Yet another approach uses positive temperature coefficient (PTC) heating elements to generate heat, but the heat output of the PTC heating elements degrade over time and may fail before other elements in the unit. This approach also runs the PTC heaters at maximum capacity whenever supplemental heat is required, regardless of how much supplemental heat is required. When more supplemental heat is generated than is required, the room heats quickly and the amount of time the supplemental heater is activated is relatively short. The room cools down while the electric heat is not activated and the electric heat module will need to be activated again. The relatively frequent cycling associated with such an arrangement may lower the life span of the PTC heaters. Thus, there is a continuing need for improved electric heating modules for room heating and air conditioning units.